3 Ahrpt Data Stream
This section provides an overview of the AHRPT data stream from the perspective of a user wishing to establish a User Station. The aim is to describe the basic characteristics of AHRPT such that users can determine the requirements of their user station and any software that might be required to manipulate the received data. Full details of AHRPT protocols and file formats are described in [RD7]
3.1 Data Structure
Data are distributed as a stream containing Channel Access Data Units (CADUs), which require further processing to produce Metop L0 products. The stream holds multiplexed data from all Metop instruments, as well as spacecraft telemetry and administrative messages. In addition to being time ordered, frame synched and randomized, CADU’s also hold Reed-Solomon decoding information and quality information.
A CADU packet can be processed further up to CVCDU, VCDU, M-PDU and Instrument Source Packets (ISPs) as CCSDS source packets; this is shown by the following diagram:
8
TD
18 Metop Direct Readout A
Figure 2 Channel Access Data Unit (CADU) Struture]
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TD 18 Metop Direct Readout AHRPT Technical Description
Futher details (e.g; PEC schemes, Reed-Solomon decoding description) can be found in [AD2].
3.2 Data Content
This section describes the various data disseminated via AHRPT.
Instrument/Application |
VCID |
APID |
Instrument/Application |
|
||||||||
|
|
|
|
|
|
|
data rate (bps) |
|
||||
AVHRR/3 High Rate |
9 |
|
|
103, 104 |
622368 |
|
||||||
AMSU-A1 |
3 |
|
|
39 |
2102 |
|
||||||
AMSU-A2 |
3 |
|
|
40 |
1142 |
|
||||||
HIRS/4 |
3 |
|
|
38 |
2907.5 |
|
||||||
SEM |
3 |
|
|
37 |
165.5 |
|
||||||
A-DCS |
27 |
|
|
35 |
7462 |
|
||||||
IASI |
10 |
|
|
130, 135, 140, |
1578860 |
|
||||||
|
|
|
|
|
|
145, 150, 160, |
|
|
||||
|
|
|
|
|
|
180 |
|
|
||||
MHS |
12 |
|
|
34 |
3924 |
|
||||||
ASCAT |
15 |
|
|
192…255 |
41032 |
|
||||||
GOME-2 |
24 |
|
|
384…447 |
399744 |
|
||||||
GRAS Occultation data |
29 |
|
|
448…511 |
60000 |
|
||||||
|
Instruments’ data sub-total: |
|
|
2719707 |
|
|||||||
|
|
|
|
|
|
|
|
|||||
Satellite housekeeping packet |
34 |
|
|
1 |
4352 |
|
||||||
Admin messages |
34 |
|
|
6 |
2008 |
|
||||||
GRAS positioning and timing data |
34 |
|
|
2, 3 |
80 |
|
||||||
|
|
VCID 34 data |
sub-total: |
|
6440 |
|
||||||
All VCIDs (excluding |
overhead) |
|
|
|
|
2726147 |
|
|||||
Protocol and RS-coding overhead |
|
|
|
|
438910 |
|
||||||
(+16.1%) on all data: |
|
|
|
|
|
|||||||
|
|
|
|
|
|
|||||||
All VCIDs (including overhead) |
|
|
|
|
3165057 |
|
||||||
Fill data |
|
|
|
|
334943 |
|
||||||
Satellite complete data rate |
|
|
|
|
3500000 |
|
||||||